1. Field of the Invention
The present invention relates to a glow plug, having a glow tube containing a heating element, in its tip portion, and also, a serially connected regulating element. More specifically, the invention relates to such a glow plug wherein the regulating element is formed of an electrically conductive material with a positive temperature-resistance coefficients, and wherein an interior pole of the glow plug is serially connected with the regulating element, the regulating element is serially connected to the heating element, and the heating element is serially connected with the glow tube tip.
A glow plug of this kind, for instance, is described in U.S. Pat. No. 4,556,781, where a glow plug has a glow tube whose tip portion contains a heating filament, and in the connection region, contains a regulating filament disposed in an insulating material.
2. Description of Related Art
Other applications have been subsequently filed with the objective to achieve a corresponding thermal decoupling between the regulating and heating filaments, whereby the function of the above glow plug was alleged to be further improved. Examples of other glow plugs of the assignee of the present application which have series connected heating and regulating elements can be found in U.S. Pat. Nos. 4,733,053; 5,091,631; and 5,172,664.
Glow plugs of this kind, known from the state of the art, have the disadvantage that they exhibit too low a stability to meet the established demands for such glow plug reliability, and that during a continuous glow action, i.e. extended glow time, with the engine in operation, they cause environmentally detrimental exhaust gases.